Tiny batteries for powering cell-sized robots

A tiny battery designed by MIT engineers could enable the deployment of cell-sized, autonomous robots for drug delivery within the human body.

Just 0.100mm long and 0.002mm thick – roughly the thickness of a human hair – the batteries can capture oxygen from air and use it to oxidize zinc, creating a current with a potential up to 1V, enough to power a small circuit, sensor, or actuator.

“We think this is going to be very enabling for robotics,” says Michael Strano, the Carbon P. Dubbs professor of chemical engineering at Massachusetts Institute of Technology (MIT) and the senior author of the study. “We’re building robotic functions onto the battery and starting to put these components together into devices.”

Ge Zhang, Ph.D. ’22 and Sungyun Yang, an MIT graduate student, are the lead authors of the paper, which appears in Science Robotics.

For several years, Strano’s lab has been working on tiny robots that sense and respond to stimuli in their environment. One of the major challenges in developing such tiny robots is making sure they have enough power.

To create robots that could become more autonomous, Strano’s lab decided to use a type of battery known as a zinc-air battery, which has a longer lifespan than many other types of batteries due to its high energy density. The battery they designed consists of a zinc electrode connected to a platinum electrode, embedded into a strip of a polymer – SU-8 – commonly used for microelectronics. When these electrodes interact with oxygen molecules from the air, the zinc becomes oxidized and releases electrons that flow to the platinum electrode, creating a current.

In this study, researchers showed this battery could provide enough energy to power an actuator – in this case a robotic arm can be raised and lowered. The battery could also power a memristor to store memories of events by changing its electrical resistance, and a clock circuit allowing robotic devices to keep track of time.

The battery also provides enough power to run two different types of sensors that change their electrical resistance when they encounter chemicals in the environment. One of the sensors is made from atomically thin molybdenum disulfide and the other from carbon nanotubes.

Robotic swarms

In this study, researchers used a wire to connect their battery to an external device, but in future work they plan to build robots in which the battery is incorporated into a device.

“This is going to form the core of a lot of our robotic efforts,” Strano says.

One of those efforts revolves around designing tiny robots that could be injected into the human body, where they could seek out a target site and then release a drug, such as insulin. For use in the human body, the researchers envision the devices would be made of biocompatible materials that would break apart once they were no longer needed.

The researchers are also working on increasing the voltage of the battery, which may enable additional applications.

The research was funded by the U.S. Army Research Office, the U.S. Department of Energy, the National Science Foundation, and a MathWorks Engineering Fellowship.

MIT
https://www.mit.edu